1. Field of the Invention
This invention relates to apparatus for testing storage batteries under load conditions. In particular, the invention relates to apparatus for automatically determining and indicating the voltage condition of the storage battery powering an electronic strobe flash unit well in advance of the time the battery normally requires to fully charge the flash unit.
2. Description Relative to the Prior Art
When a flash exposure is to be made with a camera using an electronic strobe flash unit, it is desirable to be able to determine before the exposure is made whether or not the battery is in operable condition. With cameras of the type wherein a single battery source supplies power for a built-in electronic flash unit as well as for other camera apparatus such as exposure control, film advance or shutter cocking, knowledge of the battery condition is particularly important because proper functioning of the camera cannot be assured with insufficient battery charge.
U.S. Pat. No. 4,001,639 discloses a battery condition-responsive control circuit for a camera of the type in which a single battery provides power for both a built-in electronic strobe flash unit and a film transport motor. The control circuit prevents recharging of the flash unit whenever the battery voltage falls below a predetermined value. During the interval in which the flash unit is not recharged, the failure of the flash ready light to be illuminated indicates to the photographer that the battery voltage is low and serves as a signal that the battery should be recharged or replaced. The disadvantage of this system is that the flash-ready lamp turns on only when the storage capacitor of the flash unit has been completely charged, an operation which can take more than one minute if the battery charge is low, and thus information on the battery condition cannot be obtained quickly.
Battery-check devices for cameras are disclosed in West German Patent Nos. 1,497,971 and 2,013,432 wherein the dropping of the battery voltage below a predetermined minimum value is indicated in the no-load or low-load condition of the battery. Such an indication, however, is useful only if the load on the battery is also low during operation. However, in an electronic flash unit a high load is applied to the battery during the initial charging of the storage capacitor and thus a battery-check device of this type is not suitable for rapidly indicating the condition of the battery during the capacitor charging operation.